As an exposing device included in an image forming apparatus, there is an inexpensive one-beam generating device that generates one laser beam in scanning performed once. An inexpensive control device that controls the one-beam generating device performs image input and image output (laser scanning) to and from the control device using a beam detect signal of the beam generating device as a synchronization signal. (The beam detect signal is a horizontal synchronization signal sent out by detecting a laser beam from the beam generating device in order to detect a reference of scanning of the laser beam emitted from the beam generating device.)
Further, as the exposing device included in the image forming apparatus, there is a device that performs image formation at high speed using a multibeam generating device that simultaneously emits plural laser beams in scanning performed once. In the exposing device of the image forming apparatus, if it is attempted to realize, using the multibeam generating device, image processing speed same as that realized by using the one-beam generating device, when resolution in a sub-scanning direction is high, a control device that processes image data at high speed is necessary. As an example, with the resolution in scanning of one beam set to 600 dpi, two beams are compared. When a pitch of a multibeam laser is 600 dpi, processing speed is the same. However, when the pitch is 1200 dpi, since lines are doubled, the processing speed needs to be doubled. When a control device having high image processing speed is used as the control device for the multibeam generating device, since the control device is expensive, it is likely that an increase in cost of the image forming apparatus is caused.
In an image forming apparatus that uses the multibeam generating device in order to obtain high image forming speed, there is a demand for development of a multibeam control device that can perform high-speed image processing in a relatively inexpensive control device and can maintain a high image quality.